Recently, a system has been developed which efficiently produces electricity from the sun's radiation and is described in U.S. Pat. No. 4,691,076, assigned to the present assignee. In that system, a solar array is disclosed which uses a plurality of silicon spheres that are housed in a pair of aluminum foil members to form contacts for a P-type and N-type region. Multiple arrays are interconnected to form a module of solar cell elements for converting sunlight into electricity.
An important feature when manufacturing solar cells is the uniform formation and purification of the silicon spheres. In the past, silicon spheres have been manufactured by etching irregular-shaped particles of silicon with an acid or caustic solution. Once the particles had been exposed to the acid or caustic solution, they were melted, which induced the migration of impurities contained within the particles to their surface. Eventually, silicon spheres were formed by repeating the etching and melting steps until the final product was formed.
When forming silicon spheres using the prior etching technique, a low yield resulted due to the agglomeration of the silicon particles during the melting process. Once a silicon agglomerate is formed, the material is useless and must be disposed of due to its abnormal shape. This etching technique has also been considerably expensive due to the cost of chemicals and disposal requirements of the waste products formed during processing. Additionally, it has been found that approximately 95% of the silicon particles were etched away to form the final product, resulting in high costs due to the material loss. Further, once the silicon spheres are formed, a time consuming and expensive additional step has been heretofore required to separate the spheres into size categories before implementation into solar arrays.
Therefore, a need has arisen for a method and apparatus for forming uniform spheres while simultaneously removing impurities, and for separating spheres by size during processing. Such an improved method and apparatus should also reduce chemical costs, chemical losses, and time requirements associated with previously developed sphere forming techniques.